Dies for rotary die thread rolling machines



Feb. 2, 1965 F. w. COOPER 3157979 DIES FOR ROTARY DIE THREAD ROLLING MACHINES Filed Ost. 10. 1961 4 Sheets-Sheet 3 Feb. 2, 1965 F. w. COOPER 3167,979

United States Patent Oflice 31@7,979 Patzenied Feb. 2, 1965 3,167,979 DEES RG'EARY BEE THREAD RLLENG MAQHINES Fredericir Wiiiiam Ceeper, iiirmingham, Engiand, assignor to G.K.N. Screws & Fasteners Lirniied, Birmingham, Engiand, a Briiish company Fiied Gel. 10, 1961, See. No. 144,123 Ciaims priority, applicaion Great Briiain, Geiz. Ii5, 1%(3, 35,492/60 3 Claims. (i. 80-7) This invention relates to dies for a rotary die ihread rolling machine which is of the generally known type having a rotary die provided With a thread form around its circurnference and co-operating With a stationary die which is of segmental forrn and extends around part of the circurnference of the rotary die and wherein a number of blanks are introduced one after another into the space between the rotary die and stationary die so that each blank is rolled through to the exist end of die stationary die end the thread is impressed upon the blank.

The rotary die machine has certain advanages over the other dass of thread rolling machine which is generally -termed a Hat die machine in which blanks are rolled between a pair of flat dies, one being rnovable and the other being stationary but because of t'ne relatively high cost of the rotary die, this latter machine must have a substantialiy higher output -than the fiat die rnaehine in order to be a cornmercially feasible and enonomical proposition and this question of economics is bound up with the subject of wear of the dies.

Fora reason which is explained hereinafter a rotary die machine which has a constant and uniform thread forrn around its circumference corresponding to the ihread forrn of the stationary die can be used econornically for producing certain types of screws (e.g. machine screws) because the machine can be arranged so that the wear or1 the rotary die is distributed uniforrnly around the circumference thereof. With a flat die machine When rolling any -type of screw it is inevitable that the maximum Wear on the dies oecurs at the siarting ends of the dies. I-Iowever With a rotary die machine Which has a constant and uniform thread form around its circumference there are a very large nurnber of potential starting points so that blanks can be introduced at very small intervals with the result that their thread roiling paths will overlap and thus the wear on the rotary die is spread much more uniforrnly around the circurnference and much longer die life will result.

For economic working of a rotary die machine it is therefore desirable to be able to roll large numbers of blanks for each revolution of tl1e rotor so that localised die wear is eliminated and the full efiective circurnference of the die is utilised.

However, when a blank is rolled between dies which are formed so as to produce the required thread 011 the blank it is necessary that the forrn of the dies at the start of the rolling operation is such that the material of the blank is initially deforrned at eaeh thread position With comparatively little pressure anal the die ferrn must also be sharp enough to prevent skidding of tl1e blank when it enters between d1e dies. In connection With this latter requirement it has been the practice io provide transverse serrations :1 the dies to prevent any skidding of the blank.

As the blank progresses along between the dies towards the finishing end the thread form on the dies gathers die upset material into the die groove t0 produce ti1e required thread. Certain types of screws such as machine screws, have relatively sharp threads and are 0f relatively fine pitch such that the ribs 011 the die, which correspond to the root er core form of the screw, are of sharp section and thus with ti1is type 0f screw, the thread and groove forrns of the die may be of constant section from the starting end to the finishing end because the section Will be sufficiently sharp at die starting end to permit of tl1e desired initial deforming of the material with comparative little pressure to be followed by progressive upsetting and gathering of the material as the blank progresses to the finishing end of the dies.

Hence, machine screws and similar screws having relatively sharp threads and of relatively fine pitch can be satirsfactorily produced economically 011 a rotary die thread rolling machine because the form of the die can be eonstant around the whole of the circurnference of the rotary die.

However, there is another type of screw having a diilerent -thread form which cannot be produced by ihread roliing using a die of constant forrn from one end to the other and the type of screw under consideration here is (hat in which the convolutions of the threads are spaced apart by a substantial distance. Selftapping screws which have a substantial length of flat core between adjacent thread convolutions are a good exarnple of this type of screw which, for purposes of simplicity, I term spaced thread type, where the grooves between adjacent threads is not of a sharp character. Screw nails, drive screws, drive nails and the iike also come in this category, as mentioned speeifically hereinafter, and are inciuded Within the terrn screws used herein.

With this type of screw the corresponding form of the die Will have a rib 0f flat-top, rounded, or other non sharp section to produce the groove between the threads and it is not possible, even 011 a flat die machine, to produce such screws successiully using dies of constant cross-sectional form from end-to-end and it has been found necessary to have a die of changing form such that at the starting end of the die the forrn of the rib is 015 a sharp V-section to produce the initial deforming of the material With relatively small pressure and this form changes progressively to the final required flat top or other non-sharp forrn at the finishing end of the die.

These spaced thread type of screws can be produced on a flai; die machine using die appropriate dies of Changing cross-section (as above deseribed), andl it is also possibie to produce such screws an a rotary die machine by dividing the circumference of the rotary die into an ap propriate number of separate similar dies each of Which was formed to the required changing cross-section but wi1h Ihis arrangement the blanks have to be feed-indexed between the dies so that a blank is presented at each of the starting positions of The sub-divided rotary die and ti1is inevitably leads EO localised wearing of the dies. The initial cost of such a non-uniform rotary die is very rnuch higher ihan the c0st of a rotary dies of eonstarrt thred form throughout its circumference and beeause of die localised wear, the life of the man-uniform rotary die is considerably shorter than the life of the constant thread forrn rotary die, Whilst, due to llhe necessity for feed indexing in the former, Ihre output thereof is much lower than the output from the constant form rotary die.

I: is therefore the object of the presen't invention 10 provide improvements in dies for rotary die thread rolling machines whieh will allow the production of the spaced thread type of screws economieally on such machine allowing the maximurn number 0f blanks to be fed in for each revolution of the die and making full use of the Whoie of tne circumference of ehe rotary die to distribute die wear evenly around the circurnference. Tlie maximum nurnber of blanks Which can 'oe fed in a revolution er" the rotary die Will of course depend up=on the size 05 any enlarged head at the end 0f each blank as the blanks must be spaced apart a sufiicient distance to prevent any overlap betWe-en Ehe heads, and Eo ensure that a whole number of lateral pitches is maintained between adjacent blanks.

According t the present invention I provide dies for a rotary die thread rolling machine for the production of spaced thread type of screws wherein the form of the stationary die changes gradually frorn a sharp, or relatively sharp, form at the starting end to ribs having flattops wund, or other non-sharp form at the finisbing end and the rotary die has a die form which is uniform in crosssection around the whole of its circumference, the crosssectional form of the rotary die being somewhat similar to the form at the finishing end of the stationary die but witn the crest of each rib being interrupted to give the ribs a degree of sharpness sufiicient to ensure that the material of the blank is initially deforrned with comparatively little pressure, the form of the stationary die at the finishing end being the dominant form which dictates the ultimate form of the thread which is produced on the blank.

In Order to enable a clear understanding cf the invention, the following detailed description, whieh is given with reference to the accornpanying drawings, also sontains a description 0f certain thread rolling methods as used er proposed hitherto so that the essential distinctive features of the invention can be seen against the background of the prior art as it is known to me.

In the accornpanying di'awings, which are mainly of a.

diagramrnatic riature:

FIGURE 1 shows two examples of spaced-thread type 0f screws.

FIGURE 2 shows a rotor in accordance with the invention.

FIGURES 3(a)(e) show alternate forrns of the section of the constant thread form as taken on the line 33 in FIGURE 2.

FIGURE 4 shows a preferred form of stator to be used in the method according to the invention along with the rotor of FIGURE 2.

FIGURE 5 shows sections of the thread forrn onthe lines 5W5W 5X5X 5Y5Y and 5Z5Z of FIG- URE 4.

FIGURE 6 is an exarnple of one form of point 011 a spaced-thread type cf screw FIGURES 7 and 7A illustrate diagrarnmatically the section of the point-forming part of a rotor used in producing a pointed spaced-thread type of screw, FIGURE 7A being a section on line 7A7A in FIGURE 7.

FIGURES 8, 8B, 8C and 8D illustrate digramrnatically the section of a stator to be used in conjunction with the rotor of FIGURE 7, FIGURES 8B, 8C and 8D being respectively sections on the lines 8B8B, SC8C 8D8D, in FIGURE 8.

FIGURES 9(a) and (b) show sectioned examples of further articles of the spaced-thread type.

FIGURE 10 illustrates diagrammatically the form of a roter for producing articles as shown in FIGURE 9 in accordance with the invention.

FIGURES l1(a) and (b) show enlarged sections on the line llllll (FIGURE 10) of the rotor thread form for producing the articles shown in FIGURES 9(a) and (b) respectively.

FIGURE 12 illustrates another type of spaced-thread article and the section of thread form on the rotor f01 producing such article in accordance With the invention.

Referring to the drawings, FIGURE 1 illustrates two examples of spaced-thread screws and it Will be observed that in each there is a sharp, er relatively sharp, thread 10, the convolutions of which are spaced apart by the grooves 11.

FIGURE 2 indicates diagxammaticalh a roter in ac cordance With the invention wherein the thread fo1m of the die is uniform and constant throughout the circumference of the rotor. FIGURES 3(a) to (e), show examples 0f alternative fo1ms which may be used for the section 33 015 the die form cn the rotor, it being appreciated that whatever forrn is chosen this Will be C011- stant througl1out the whole circumference 0f the roter. These exarnples are also given to ill'ustrate what is meant by the interruption 0f the crest of each rib to give it a degree of sharpness which will be sutficient to ensure, in cooperation with the opposed stator, the initial deforming of the metal of the blank Und1 relatively small pressure.

Referring to FIGURE 3(a) the die forrn has ribs 21 separated by main grooves 22, and each 1'ib 21 is somewaat similar to the form at the finishing end of the stator (the Section YY, ZZ, FIGURE 5 is representative of the finishing end forrn of the stator as is mentioned hereinafter) but, the ernst 0f the rib 21 is interrupted by a relatively shallow groove 23 which modifies the flat t0p form and so creates the required amount of sharpness.

PIGURES 3(b) and 3(c) shovv alternative forrns for the groove 23 and in FIGURE 3(d) the groove 23 l1as a partially convex base giving the etfect alrnost 0f two grooves. FIGURE 3(c) illustrates how, in some cases, more than one groove -may be employed.

the crest of the. rib 21 to achieve the desired degree of sharpness. The aetual formation chosen Will be a matter of choice, in practice, depending upon the actual thread form which is being rolled on the blank and taking into account other factors such as the material and dimensions of the blank. A certain amount of trial and error may be required to achieve the best formation of rib 21 for any particular case.

A further consideration is that the fonn of interruption on the crest cf the rib 21 must be such that it will not interfere with the final thxead form on the screw and the die form at the finisbing end of the stator must be the dominant form which dictates the final thread form 011 the screw, such as in FIGURE l.

It has been found in practice that a, groove or grooves 23, relatively shallow, as compared with the deptl1 of the thread-forrning groove 22, Will not in any Way interfere with the aotion of the rib form at the finishing end of the stator and this rib form rnaintains the overall comtrol cf the final gathering and positioning of the metal 0f the blank to give the desired flat bottom grooves 11 (see FIGURE l).

In fact, tests so far carried Gut, show that screws produced using dies accmding to the invention have a betten thread form than do those produced by-conventional rolling dies because it has been recognized in the past that conventional thread rolling dies clo not produce true flatbottom grooves 11 on a screw (See FIGURE l) but tend to produce a groove which has slight concavity. It has been observed that screws produced 011 dies according to the invention have grooves 11 which are more nearly true flat bottomed than hitherto and Whilst the reason for this is not fully understood, it is clear that the presence of the groove or grooves 23 has some benexicial effect in comtrolling the flow of the metal of the blank to make it follow more faithfully the shape whicl1 is dictated by the die form at the finishing end of the stator.

Whilst the form of the stator may be the same as has been previously used in connection With a sub-divided rotary die it is preferred t0 use the improved fonn of stator* which is illustrated in FIGURES 4 and 5.

In FIGURES 4 and 5 the sections WW XX YY and Z-Z depict the changing form of the die cross section frorn the starting end to the finishing end.

As will be observed at the finishing end cf sections YY to ZZ, the form is similar to the finishing form in a conventional stator With flat-top ribs 24 separated by relatively deep grooves 25 but at the starting end of the stator instead of the sharp ribs there are provided ribs 26 which are almost of flat-top forn1 except that the crest of each rib is interrupted by a relatively sllallow gr'oove 27 to give the rib the degree of sharpness requi1ed t0 ensure the initial deformation of the metal of the blank under rela- In all Gases the purpose of the one or more grooves is to interrupt tively small pressure. As will be appreciated, any of the alternative forms of interruption illustrated in FIGURE 3 may be used at this starting end of the stator die so as to provide the ribs 26 with the desired degree of sl1arpness.

As Will be observed from the section XX, the groove 27 01' other form of interruption gradually decreases until at the commencement of the finishing end section YY, the interruption 27 has disappeared and the rib merges into the full flat-top section 24.

Previously it has always been considered essential to provide some ineans to prevent skidding of the blank when it is first introduced between the dies and the practice adopted hitherto has been to provide transverse serrations across the face of the die over the starting portion thereof thus roughening the surface of the die and providing the necessary grip to prevent skidding of the blank. Although this has been an essential reqnirernent it has always been regarcled as undesirable owing to the fact that the presence of the serrations does create flaws in the finished thread form but hitherto there has been 110 satisfactory way of avoiding the requirement for serrations or sorne sirnilar form of roughening at the starting end cf the dies.

However With the improved form cf stator die described above, it is fonnd that serrations can be eliminated or substantially reducedas there is considerably rnuch less danger for skidding of a blank when it is introdnced between dies in which the stator die has the form above described.

The presence of a somewhat similar form of die on the rotor also enhances this eifect and the elimination of serrations on dies further reduces the cost of manufacture and eliminates the possibility of any fiaws occurring in the finished thread form of a screw.

FIGURE 6 illustrates a form cf spaced-thread type screw having a pointed end 28 With the thread forrn coutinued down along this pointed end and in the production of pointed screws of this type in accordance With the invention, the roter would need to be provided With a point-forming portion With also a point forming portion being provided 011 the stator and for this particular application, a rotor and stator as illustrated diagrammatically in FIGURES 7 and 8 may be used.

The stator depicted in FIGURE 8 has a point-forming portion which is cf generally known form and as Will be seen from sections BB CC and DD this point forming portion changes gradually in form from the relieved section at B-B to the pronounced rib form 29 at DD Wh=ich dictates the actual form of the point. It will be appreciated that in FIGURES 7 and 8 the tl1read form of the dies has not been illustrated in the sections.

The cooperating point-forming portion on the rotor of FIGURE 7 is of eonstant section throughout the circumference 0f the roter and as illustrated in the section AA this point-forming portion is snbstantially similar to the finishing section DD on the stator having the projecting rib 30 which cooperates With the rib 29 0n the stator to form a desired point.

FIGURE 9 depicts in cross-section two further forms of articles which corne under the classifieation of spacedthread type the one shown in FIGURE 9(a) being a section thro=ugh a drive screw having sharp ribs 31 cf large helix angle separated by grooves 32 each of Whieh has a bottom having slight convexity The article illustrated in FIGURE 9(b) is a drive nail having pronounced ribs 33 separated by relatively wide grooves 34 Which have a pronounced concavity.

The form of roter suitab-le for producing these two articles is depicted in FIGURES and 11, the rotor of FIGURE 10 having a constant thread form throughout its eircumference and as Will be seen in FIGURE ll(a), the section X-X of this thread form for producing the drive screw of FIGURE 9(a) would have ribs 35 separated by relatively deep grooves 36 and eaeh of the ribs 35 having its crest interruptedl by a relatively shallow groove 37 to give the desired degree of sharpness to the rib.

The cross-section XX of the thread forrn for producing the article of FIGURE 9(b) is depicted in FIG- URE 11(b) and in this case there are ribs 38 separated by grooves 39 and each of the ribs 38 having its crest interrupted by a shallovv groove 40 to give the desired degree of sharpening to the crest of the rib.

A further article of spaced-thread type is illustrated in FIGURE 12 together With a view showing the c1osssection of the constant thread form whioh would be provided on a roter for produoing this article.

The article itselt is a drive nail having a thread which takes the fonm of a series of annular ribs 41 separated by annular flat bottorn grooves 42 and the cross-sectional form of the rotor f0r producing such an article would have ribs 43 separated by grooves 44 cf asymmetrical crosssection, the crest 01": each rib 43 being interrupted by a groove 45 to give the desired degree of sharpness.

In addition to the manufacturing aclvantages With a rotor formed in accordance With the invention as the cross-sectional thread forma is uniform throughout the circumference, the roter ean be reversed end-for-end when any appreciable wear has taken platze over one side thereof so as to make use of the Whole of the circumferential face of the die and thus achieve a further increase in the effective life of the roter.

By virtue of the uniform thread form on its circumferenee, manufacture of the roter is considerably simplified and thus rendered less expensive than a sub-divided roter and as the blanks ean be fed in at close intervals, the machine Will give a high output of screws per revolution of the rotor witl1 wear heilig distributed much more uniformly around the Whole circumference ot the rotor.

What I clairn then is:

1. Dies for the production of spaced thread type screws in a rotary die thread rolling machine of the type Wherein blanks are introduced in suocession into the space between a rotary die having a thread form around its circurnference and a co-operating stationary die 0f segrnental form, said dies comprising a stationary die having on its face which co-operates with the rotary die a thread form comprising alternate ribs and main grooves extending from the starting end to the finishing end of the die, each rib having a sharp forma at the starting end and changing gradually from such sharp form t o a flat-top forn1 at the finishing end, and a rotary die having around its circumferenee a thread form compns ing alternate n'bs and main grooves, each 1'ib having a f01'm, throughout its length, which is sirnilar to the flattop form at the finishing end of a rib on1 the stationary die, but each rib 011 the rotary die having its crest provided with at least one groove runm'ng the length of the rib and of depth Which is zrelatively shallow as compared with the depth cf the main grooves on the rotary die.

2. Dies for the production of spacecl thread type screws in a rotary die thread rolling machine of the type Wherein blanks are introduced in suocession into the space between a rotary die having a thread form a.ronnd its circurnference and a co-operating stationary die of seg mental fern], said dies comprising a statienary die having on its face wl1ich co-operates With the rotary die a thread form comprising alternate ribs and main grooves extending iirom the starting end t0 the finishing end of the die, each rib having a flat top form at the finishing end and at least one groove extending fr0m the starting end of the rib along its length towards the finishing end and gradually decreasing in depth fron1 the starting end until it disappears at a position short of the finishing end of the rib, the depth of such groove at the starting end being relatively shallow as compared With the depth of the main groeves, and a rotary die having around its circumferenoe a thread form comprising alterxiate ribs and main grooves, each ribhaving a form, throughout its length, which is similar to the flattop form at the finishing end of a nib 011 the stationary die, but each rib on the rotary die having its crest provided With at least one groove running the 1ength of the rib and of depth which is relatively shallow as compared with the depth of the main grooves on the rotary die.

3. Dies for the producbion of spaced thread type screws in a rotary die thread rolling machine of the type Wherein blanks a1'e introduced in succession into the space between a rotary die having a thread forrn around its circurnference and a co-operating stationary die of segmental form, said dies comprising a stationary die having 011 its face whieh co-operates with the rotary die a thread form comprising alternate ribs and main grooves extending from tl1e starting end to the finishing end of the die, each rib having a sharp form at the starting end and changing gradually from such sharp form to a flattop form at the finishing end, and a rotary die having around its circumference a thread forn1 comprising alternate ribs and main grooves, each rib having a form, throughout its length, which is similar to the flat-top f0rm at the finishing end of a rib 011 the stationary die, but each rib on the rotary die having its crest provided with at least one groove running the length of the rib and of depth which is relatively shallow as compaxed with the depth of the main grooves 011 tlle rotary die, said rotary die also having a pointforming portion which extends around its oircumference and is of constant form throughout its length.

References Cited by the Examina- UNITED STATES PATENTS 329,737 11/85 Harvey 807 425,035 4/90 Jones 809 1684799 9/28 Kochendorfer 807 2923186 2/60 Pierson 807 WILLIAM J. STEPHENSON, Primary Examiner.

LEON PEAK, Examz'ner. 

1. DIES FOR THE PRODUCTION OF SPACED THREAD TYPE SCREWS IN A ROTARY DIE THREAD ROLLING MACHINE OF THE TYPE WHEREIN BLANKS ARE INTRODUCED IN SUCCESSION INTO THE SPACE BETWEEN A ROTARY DIE HAVING A TREAD FORM AROUND ITS CIRCUMFERENCE AND A CO-OPERATING STATIONARY DIE OF SEGMENTAL FORM, SAID DIES COMPRISING A STATIONARY DIE HAVING ON ITS FACE WHICH CO-OPERATES WITH THE ROTARY DIE A THREAD FORM COMPRISING ALTERNAE RIBS AND MAIN GROOVES EXTENDING FROM THE STARTING END TO THE FINISHING END OF THE DIE, EACH RIB HAVING A SHARP FORM AT THE STARTING END AND CHANGING GRADUALLY FROM SUCH SHARP FORM TO A FLAT-TOP FORM AT THE FINISHING END, AND A ROTARY DIE HAVING AROUND ITS CIRCUMFERENCE A THREAD FORM COMPRISING ALTERNATE RIBS AND MAIN GROOVES, EACH RIB HAVING A FORM, THROUGHOUT ITS LENGTH, WHICH IS SIMILAR TO THE FLATTOP FORM AT THE FINISHING END OF A RIB ON THE STATIONARY DIE, BUT EACH RIB ON THE ROTARY DIE HAVING ITS CREST PROVIDED WITH AT LEAST ONE GROOVE RUNNING THE LENGTH OF 